Symptoms Associated with Low Threshold Lead Poisoning Among Roadside and Organized Panel Beaters in Enugu Metropolis, Nigeria

Background. There is no safe level of human exposure to lead (Pb). Detecting common early symptoms of low threshold Pb poisoning can help to prevent the damaging effects of higher doses and chronic low dose exposures. Panel beaters or auto body mechanics are exposed to Pb through their occupational duties. Objectives. The present study aimed to determine common early symptoms associated with lower threshold Pb poisoning among roadside and organized panel beaters in Enugu Metropolis, Nigeria. Methods. This was a comparative cross-sectional study of 428 panel beaters in Enugu metropolis. A multi-stage sampling method was used to select 214 respondents each from the roadside and organized sectors. A semi-structured interviewer-administered questionnaire was used for data collection. Samples were collected under aseptic procedures. Blood Pb samples were extracted using the conventional wet acid digestion method and analyzed using a flame atomic absorption spectrometer (wavelength 283.3 nm). Comparative analysis was performed using the chi – square and Mann-Whitney U test. Statistical significance was set at P < 0.05. Results. Median Pb levels were 3.0 ug/dL and 16.0 ug/dL among roadside and organized panel beaters, respectively, with a significant difference. Numbness of limbs (P = 0.010) and fatigue (χ2 = 5.294, P = 0.023) were found to be associated with roadside panel beaters, while weakness (χ2 = 6.185, P = 0.019) and fatigue (χ2 = 4.206, P = 0.046) were associated with organized panel beaters. Conclusions. Nonspecific constitutional symptoms were common early symptoms of Pb poisoning irrespective of workplace occupational practices. These symptoms will help in early detection and control of occupational lead exposures. Participant Consent. Obtained Ethics Approval. Ethics approval was obtained from the Health Research Ethics Committee of the University of Nigeria Teaching Hospital, Ituku Ozalla, Enugu. Competing Interests. The authors declare no competing financial interests.


Introduction
Panel beaters and auto body mechanics are automobile technician subspecialties whose occupational practices include repair, cutting, soldering, welding and spray painting which exposes them to lead (Pb) poisoning. Other practices include repair of chips and scuffs, polishing and waxing, glass and interior repair, and wheel refinishing. 1 Panel beaters operate in both the informal sector (operating along roadsides) and the formal organized sector. Organized panel beaters are those working in sectors with rules and requirements set by the government and the sector is governed by acts such as the Factories Act, 2 labor laws, and Employee Compensation Act; 3 they practice with safety precautions and have fixed working hours. The informal sector is a private unincorporated enterprise operating along roadsides with no regular system of data availability. 4 Toxicities manifest as overt clinical symptoms primarily detected at high doses, thereby underestimating the actual burden of Pb toxicity. 5 They occur in severe multi-systemic clinical forms: abdominal colic, joint and muscle pain, wrist and ankle drop, fine tremors, diminished visual intelligence and motor coordination, short term memory loss, irritability, encephalopathy, lethargy, delirium, convulsions, coma, fatigue, weakness, excessive tiredness, constipation, anorexia, persistent vomiting, impotence, infertility and reduced sex drive. 1,6,7,8,9 These toxicities are common at blood lead levels of 40 µg/dL and above. 10, 11 The American Conference of Governmental Industrial Hygienists (ACGIH) has stated that blood lead levels (BLLs)

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should be controlled at 20 ug/dL. 12 Low Pb levels refer to exposure levels below which Pb poisoning is apparent, non-specific, asymptomatic or subclinical, but not without harmful effects. 13 Prevention measures and campaigns that lead to the removal of leaded paints in 1921 and leaded gasoline in the 1980s-90s resulted in significant lowering of Pb levels. 1, 14 In 1978, the United States Occupational Safety and Health Administration (OSHA) required interventions for adult workers at a BLL of 10 µg/dL and above. 15 In 2012, the Centers for Disease Control and Prevention (CDC) set a threshold for elevated BLL for children at 5 µg/dL. 16 Despite progress in the control of occupational Pb exposures and reduction of Pb exposures in work environments, studies have found the health effects of chronic exposures to Pb at lower doses or thresholds to include hypertension, a decrease in renal function, cognitive dysfunction and other nonspecific symptoms. 17,18 This indicates that there is no safe level of Pb exposure, but as Pb levels increase, the severity of damage to target organs and consequent symptoms also increases. 6 The World Health Organization (WHO) identifies Pb as one of 10 chemicals of public health concern. 13 An estimated 120 million people around the world have BLLs greater than 10 ug/dL. 19 In 2017 the Institute of Health Metrics and Evaluation (IHME) attributed 1.06 million deaths and 24.4 million disability-adjusted life years (DALYs) worldwide to Pb exposure. 13,20,21 In Nigeria, Pb toxicity accounts for 1.6 deaths per 100 000 and 46.82 DALYS per 100 000 population. 20,21 The IHME also estimated that in 2016, Pb exposure accounted for 63.2% of the global burden of idiopathic developmental intellectual disability, 10.3% of the global burden of hypertensive heart disease, 5.6% of the global burden of ischemic heart disease and 6.2% of the global burden of stroke, with the highest burden in developing countries. 13,20,21 Even with severe underreporting, a study in the USA found that reducing occupational Pb limits produces annual societal benefits of almost $40,000 per highly exposed worker in the USA, taking into account the effects of direct and indirect costs and omitting health effects. 22 There is increasing scientific evidence of the harmful effects of Pb poisoning in nonspecific subclinical forms in addition to specific clinical forms. The present study will add to the existing literature on early common symptoms of Pb poisoning at reduced thresholds, thereby preventing the damaging health effects of low dose chronic exposure and high dose toxicities in low-income countries or industries where routine Pb monitoring may be difficult. This study will further emphasize the benefits of regular screening, and early diagnosis and treatment to mitigate this occupational hazard. For the most part, the diagnosis of Pb poisoning in adult workers is based on integration of data obtained from patient history, physical examination, laboratory tests and tests of specific organ function. This will help to prevent the development of higher BLLs above which overt severe clinical symptoms are seen.
The aim of the present study is to examine common symptoms associated with Pb poisoning at lower thresholds among roadside and formal sector panel beaters in Enugu Metropolis, Nigeria.

Methods
The study area was Enugu metropolis which is the capital of Enugu State in the southeast geo-political zone of Nigeria. The metropolis is constituted by three Local Government Areas in Enugu State which are Enugu North, Enugu South and Enugu East and is inhabited primarily by the Igbo ethnic group. 23 According to the 2006 National Population census, Enugu Metropolis had a total population of 722,664, representing 22.2% of the Enugu State population and 0.51% of the total Nigerian population. 23,24 The main occupation is trade, followed by services like transportation and public service. 25 The transportation business includes workshops where panel beaters engage in vehicle body repair. Roadside panel beaters operate mainly alongside roads and close to vehicle spare parts markets. They operate as unions, without government regulations and with no standard safety practices, while the organized panel beaters are governed by government acts like factory and labor acts, worker compensation laws, and standard safety precautions.
This was a comparative cross-sectional study of roadside and organized panel beaters in Enugu metropolis conducted from November 2018 to April 2019. Panel beaters and trainees who had spent over one year in the occupation and who were willing to participate in the study were included, while those on chelation therapy, on allopurinol, were severely ill or with chronic diseases were excluded. The questionnaire was pre-tested in Enugu East. About 20 samples were collected from both sectors for the pretest. The observed shortcomings in relevance and scope of questions were corrected before final administration of the questionnaires to the respondents. Data and samples were collected using research assistants comprised of three resident doctors and three phlebotomists. They were trained for two days, for two hours per day on sample collection procedures and questionnaire administration, communication and follow-up skills, study objectives and ethical issues involved in the research. Blood for Pb sampling was collected under aseptic procedures and analyzed at the biochemical laboratory unit of the Project Development Institute (PRODA), Enugu using a flame atomic absorption spectrometer at 283.3 nm wavelength. The PRODA is an industrial research institute under the Nigerian Federal Ministry of Science and Technology operating under a quality management system. Blood sample collection was done in an enclosed well-screened location.
The venipuncture system was used to perform venipuncture and 2-3 ml of blood drawn into an edetic acid (EDTA) vacutainer bottle for BLL estimation. The samples were transported immediately to the laboratories using a Giostyle cold box (Giostyle, Urgnano, Italy) after each day, accompanied by 5-and 10-ml syringes, bleach, and gloves for maintenance of universal precautions. The blood samples were diluted to 10 ml using deionized water to obtain reliable results. The diluted samples were acidified with trichloroacetic acid (TCA) and Pb was extracted using a conventional wet acid digestion method. The aspirated extracts were analyzed by a flame atomic absorption spectrometer at a wavelength of 283.3 nm. Process controls involving quality of testing, sample handling, standard safety practices, verification and validation of results were ensured by the laboratory for quality control. The analytical accuracy was checked using an internal quality assessment method through machine calibration with a standard Pb stock solution, standardization of machine and appropriate wavelength setting. Data were entered and analyzed using the Statistical Package for the Social Sciences (SPSS) version 20.
Categorical variables were summarized using frequencies and proportion, while continuous variables were summarized using median and range for skewed data. Blood lead levels were categorized using a cut-off of < 10 µg/ dl (unexposed), 10-40 µg/dl (normal, acceptable) and >40 µg/dl (dangerous), respectively. 15,29 The proportion of panel beaters with a BLL of 10 ug/dL and above was determined. Comparison of variables was managed using the Mann Whitney U-test and Chi-square test. Level of significance was set at 0.05.

Ethics approval
Ethics approval was obtained from the Health Research Ethics

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Committee of the University of Nigeria Teaching Hospital, Ituku Ozalla, Enugu. Permission was obtained from unions of panel beaters and organized panel beaters in Enugu State. Informed consent was obtained from participants. The outcomes of the analyses were relayed to the workers immediately. Some were informed by telephone while some results were delivered to their workplace by hand. Those with high blood levels were counseled and educated on the implications of their results, exposure sources, and safety and preventive measures. Those with BLLs between 10-40 µg/dL were told to retest in 6 months, those with BLLs 40-50 µg/ dL were told to retest in 2 months, while those with BLLs > 50 µg/dL were advised to stop their occupational exposure and retest in one month. Chelation is recommended at BLL > 45 µg/dL.

Results
The mean ages (±standard deviation) were 31.1 ± 10.3 years and 37.9 ± 12.1 years for roadside and organized panel beaters, respectively. All the respondents from both sectors were male and from the Igbo ethnic group. The majority of the respondents from the roadside and organized sectors had a secondary education. Many of the roadside panel beaters were single compared to organized panel beaters who were more likely to be married. Roadside workers tended to earn more than their counterparts in the organized sector (Table 1).

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repair, while spray painting was the least common. The majority of the workers worked more than 8 hours per day, with roadside workers working more hours compared to the organized sector. Most workers in the roadside sector worked 2-3 days per week, while the organized sector worked more than 3 times per week. The majority of workers in both sectors had worked for 1-10 years ( Table 2).
The median BLL for the roadside and organized panel beaters was 3.0 µg/dL and 16.0 µg/dL, respectively. The prevalence of BPb at 10 µg/dl and above was 36.9% and 64.5% for roadside and organized panel beaters, respectively. The differences between the two groups were found to be significant. The majority of the panel beater BLLs were within the acceptable limits for occupational workers, although they were greater among the organized group (Table 3). Among the roadside panel beaters, numbness and fatigue were symptoms associated with BLLs of ≥ 10 µg/dL, while weakness and fatigue were associated with BLLs of ≥ 10 µg/dL among organized panel beaters (Table 4).

Discussion
Due to the effects of Pb poisoning at varying thresholds, there is no entirely safe BLL. As Pb levels increase, the severity of damage to target organs and consequent symptoms increase. 6 The current study found that median BLLs were within the normal and acceptable levels for roadside and organized panel beaters, with a higher prevalence of Pb levels ≥ 10 µg/dL among organized sector workers compared to roadside sector workers.  38 These studies similarly report the presence of nonspecific symptoms among occupational workers following Pb exposure. The symptoms reported by respondents in the present study are in keeping with the current understanding that low dose chronic Pb exposures cause damage to body systems and there is no safe level of Pb. 6,39 Recognition of these nonspecific symptoms can help in the prevention of further Pb poisoning among occupationally exposed workers.

Study limitations
This study is a cross-sectional study, and the symptoms experienced were limited to the period of study. All the participants in the present study were male. In addition, the study is specific to one area and therefore the results are not generalizable.

Conclusions
Nonspecific constitutional symptoms are the most common manifestations of occupational Pb poisoning at lower dose exposures. These symptoms occurred irrespective of BLLs content among roadside and organized panel beaters. Symptoms included weakness, fatigue, nausea and numbness of the limbs. Employers and workers should be made aware of the importance of these nonspecific symptoms in their occupational practices through health education. Routine biological and environmental monitoring is recommended to employers to keep Pb exposures to below 10 ug/dL. Other safety practices and engineering controls should be enforced in the workplace.

Funding
This study was funded as part of employment.